Basics of a Capacitor

An electric charge is stored in an electric field by a simple electric device called a capacitor. A dielectric material separates the two conductive plates that jointly make a capacitor. An electric potential difference arises from the plates becoming oppositely charged when voltage is supplied. By attaching a wire from a high-voltage electrostatic generator to a volume of water in a portable glass jar, Ewald Georg von Kleist of Pomerania, Germany, discovered that charge could be stored in October 1745. To improve the charge storage capacity, Daniel Gralath was the first person to connect multiple jars in parallel. After looking into the Leyden jar, Benjamin Franklin concluded that the charge was kept on the glass. Porcelain capacitors were used in the early wireless devices for obtaining high voltage and high frequency. The earliest electrolytic capacitors were created by Charles Pollak (born Karol Pollak), who discovered that an aluminum anode’s oxide layer was constant in an alkaline or neutral electrolyte even after the power was cut. Later in 1957 H. Becker invented electric double-layer capacitors which are now recognized as supercapacitors. Later, the MOS capacitor was widely used as a storage capacitor in memory chips. Dr. Robert Dennard combined one MOS transistor for each capacitor to create the present DRAM structure in 1966.

Capacitors

What is a Capacitor?

An electronic device containing two terminals that stores and distributes electrical energy is called a capacitor.  The main purpose of a capacitor is to store electrical energy for a certain time and then release it when needed. Capacitors can be divided into many kinds depending on certain requirements like voltage, capacitance, and physical structure. Each of them are designed for specific purposes.

When studying about capacitors, one must be familiar with the idea of capacitance. Capacitance is the amount of charge that a capacitor can store per unit of voltage. A capacitor can only keep a certain amount of charge at a particular voltage which is measured in capacitance. In other words, capacitance is the quantity of charge collected in the capacitor for developing one volt potential difference across it. The charge accumulated in the capacitor and potential difference is directly related to each other.

Q โˆ V

Or, Q = CV [Equation 1]

Here, charge is denoted by Q and V is denoted by V. The proportionality constant C is called the capacitance. This capacitance is affected by three major factors which are, the area of the conductive plates (A), perpendicular distance between these plates (d) and the dielectric constant or the permitivity of the medium i.e.

C = ฮตA/d [Equation 2]

C is measured in Farads (F). Capacitors are famous in various fields like signal processing, energy storage and timing applications.

How do Capacitors Work

Capacitors simply work on the basis of principles of electrostatics. When a voltage is applied to the capacitor, it absorbs electric charge. This charge absorbed  is then sent back into the circuit when necessary. A basic capacitor is made of two parallel metal plates separated by a dielectric material. When a source of voltage is applied to the capacitor, the wire or plates that are connected to the positive terminal of the source receives positive charge, while the plate connected to the negative terminal receives a negative charge. Charges cannot pass directly from one plate to the other due to the dielectric present between them.

This causes the charge levels of plates to vary, which in return causes a potential difference between them. The charge collection process in the capacitor plates is a slow process and changes continuously over time rather than all at once. The potential develops across the capacitor and increases exponentially until it reaches the voltage of the source. The quantity of charge kept in a capacitor is proportional to its capacitance and the being applied. To understand how a capacitor works in a circuit, we must consider the following points.

  • Charging of a Capacitor: When a capacitor is connected to a source, charge begins to collect on the plates. The rate of charging is initially fast. However it slows down as the capacitor reaches its maximum charging capacity. The time it takes to charge to approximately 63% of its full charge is called the time constant (ฯ„), which depends on the capacitance and resistance in the circuit.
  • Discharging a Capacitor: Now if the source is disconnected, the capacitor will start to give up the stored energy. The discharging rate is exponential with the decreasing voltage over time. This time of discharge is also controlled by the time constant of the circuit.

Different Types of Capacitors and Their Uses

Below are some of the most common types of capacitors and their applications.

  •  Ceramic Capacitors

Ceramic capacitors are the most widely used capacitors. These are non-polarized capacitors and are cheap and of small size, which make them affordable. Ceramic capacitors are regarded as best ones for operation. They are made using a ceramic material as the dielectric. This dielectric has poor conductivity and effectively supports electrostatic fields. Ceramic capacitors are mainly used to generate high-frequency such as radio frequency (RF) circuits, signal filtering, power supply decoupling and timing circuits.

  •  Electrolytic Capacitors

Electrolytic capacitors have positive and negative terminal and hence called polarized capacitors. An electrolytic capacitor is a type of capacitor that uses an electrolyte that gives more capacitance than normal capacitors. The electrolyte used is frequently made up of aluminum, tantalum, or a few other metals. This high capacitance produced is applied to send low frequency signals. They are used in power supply filtering, audio amplifiers, power-factor correction and energy storage applications. It should be noted that they are not suitable for high-frequency applications. (Read about Electrolytic cell)

  • Tantalum Capacitors

Tantalum capacitors are electrolytic capacitors where tantalum metal is used as the anode. Tantalum is originally a shiny and silvery metal. The metal doesn’t rust or corrode at temperatures below 150 degrees Celsius.  It is readily available in nature and has high heat and electrical conductivity. It has a relatively high melting point of 3017 ยฐC and a boiling point of about 5458 ยฐC.  This metal is highly tolerant to all acids at normal temperatures except hydrochloric acid. Tantalum capacitors give a stable capacitance. They are small in size and can withstand greater voltages than other electrolytics. They are used to create portable electronics, military, and aerospace applications.

  • Film Capacitors

The film capacitor is a non-polarized capacitor.  Its dielectric is made up of thin plastic films. These plastic films may be metalized and sold as “metalized capacitors”. These capacitors can also be referred to as metalized or plastic capacitors. These films are sometimes simply layered to form a \ rectangular shape like a candy. Polypropylene (PP), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), and polyphenylene sulfide (PPS) are the most frequently used dielectrics. The main benefit of using a film capacitor is its extremely small distortion factor and outstanding frequency characteristics.  Audio equipment, signal processing, and motor run capacitors are some of the applications of film capacitors

  • Supercapacitors 

Supercapacitors are also called ultracapacitors. This capacitor is known as an ultracapacitor because it has a larger capacitance than other types of capacitors. They have low voltage boundaries. These components have been chosen over normal capacitors due to their increased power output. These components require less electricity and are completely safe and simple to use. Supercapacitors are used in applications that require rapid charge and discharge cycles like energy storage systems, power backups,  regenerative braking in electric vehicles and memory backup.

  • Mica Capacitors

Mica capacitors are capacitors that use mica as its dielectric. There are two types of mica capacitors: clamped and silver mica capacitors. Clamped mica capacitors are now outdated due to their poor results. Silver mica capacitors are employed alternately. They are constructed by placing mica sheets wrapped with metal on both sides. This structure is then covered in epoxy to protect it from the elements. Mica capacitors are frequently used in designs that require stable, reliable capacitors with fairly small values. They can operate at high frequencies, and their value does not fluctuate significantly over time. Mica minerals are extremely stable electrically, chemically, and mechanically. RF circuits, oscillators, and high-precision signal filtering use these capacitors

Common Applications of Capacitors in Everyday Electronics

Capacitors play an important role in the daily functioning of many electronic devices. Here are some of the important applications of capacitors:

  •  Power Supply Filtering

Capacitors are frequently used to balance the variations in voltage of a power supply. When AC gets converted to DC, ripples occur that create fluctuations in voltage. Capacitors are connected in parallel with the power source to cancel out ripples and regulate the voltage. This makes sure of the smooth functioning of electronic circuits.

  • Signal Coupling and Decoupling

Capacitors can be used in coupling and decoupling purposes to control signal transmission between different stages of the circuit. Capacitors in coupling block DC and allow AC signals to pass. Capacitors are used in decoupling to minimize noise and regulate voltage levels, enabling uniformity of signals.

  •  Timing Circuits

A combination of capacitors and resistors are generally used in timing circuits like oscillators and pulse generators. Precise time delays or frequencies are generated by using the charging and discharging nature of capacitors.

  •  Engine Starting and Running Capacitors

Capacitors are used in engines to improve their starting and run them smoothly. Starting capacitors give a short-term rise of power to help the engine initiate while running capacitors make sure of a constant electrical supply to the engine and allow it to operate properly.

  •  Energy Storage

Capacitors are used as energy storing devices. These capacitors can store a lot of electricity and release it quickly when needed. Hence, they are used to develop regenerative brakes in electric vehicles and create memory backup in devices such as computers.

How to Calculate Capacitance: A Step-by-Step Guide

Before the calculation, sound knowledge of material properties and setup of capacitors in a circuit is foremost.. The formula for capacitance is given by:

C = ฮตrฮต0A/d

Where C is the capacitance, ฮตrโ€‹ is the relative permittivity of the dielectric material, ฮต0 is the permittivity of free space (8.854 ร— 10โปยนยฒ F/m), A is the area of the plates and d is the distance between the plates in meters.

Example Calculation:

If a capacitor is given with two parallel plates of area 0.01 mยฒ and    having perpendicular distance 0.001 m, find the capacitance where the dielectric has the relative permittivity of 2.5.

Solution:

Given,

Area of plates (A) = 0.01 mยฒ

Distance between plates (d) = 0.001 m

C = (2.5)(8.854ร—10โˆ’12)(0.01)/0.001

=2.21ร—10โˆ’12F

=2.21โ€‰pF

From this example we can study how the physical properties like area of plates, their perpendicular distance and dielectric affects the capacitance.

Series and Parallel Capacitor Configurations Explained

Capacitors can be connected in series or parallel ways. This arrangement of capacitor also affects the total capacitance of the circuit.

  •  Series Capacitor Configuration

If capacitors C1, C2, C3 … are connected in a series, the total capacitance (Ctotal) is given by the formula:

1/Ctotal=1/C1+1/C2+1/C3+โ€ฆ

As these capacitors have fractional addition in series, the resultant capacitance will be decreased than that of the individuals. The voltage is divided across the capacitors in series circuit. However, the charge remains the same on each capacitor.

  • Parallel Capacitor Configuration

If capacitors C1, C2, C3,… are connected in parallel connection, the total capacitance (Ctotal) is given by the formula;

Ctotal = C1+C2+C3+โ€ฆ

Thus resulting capacitance is higher than the individual capacitors. In parallel circuits, each capacitor receives the same voltage, but the charge varies between capacitors.

The Role of Dielectrics in Capacitor Functionality

The dielectric material used between the plates has huge effects on the functioning of a capacitor. A dielectric is similar to an insulator as it decreases the flow of an electric field between plates but preserves the same applied voltage. This makes capacitor able to hold more charge.

Different dielectrics like air, ceramic, paper etc. have different properties of lowering electric fields which makes different values of dielectric constant in different medium. This makes capacitors able to run in a wide range of voltages and conditions. The relative permittivity of dielectric (ฮตr) determines its ability to increase the capacitance of a capacitor.

Capacitor Safety Tips: Handling and Precautions

Capacitors are not that harmful to handle. However there are several precautions to consider for safe operation and to avoid mishaps.

  •  Capacitors should be discharged before operating them in the circuits to prevent electric shocks.
  • One should never exceed the maximum voltage rating of a capacitor. This can cause the capacitor to explode or not function.
  • We have to make sure that they are not shorted while testing. This can avoid any possible harm.
  • Capacitors should be stored in a cool and dry place to prevent it from damage.
  • Proper disposal of damage or outdated capacitors is required as per the local regulations. Some of the capacitors like electrolytic and supercapacitors can emit hazardous materials if not disposed properly.

Conclusion

Today modern electronics are impossible without capacitors. They are used mostly in energy storage, signal processing, power filtering, and various other applications. Capacitors are more like a base for most of the latest devices we in our daily basis. There are some fundamental operating principles that must be understood to use them in various applications. Knowledge of how capacitors work, calculating their capacitance and their behavior in circuits can help to develop a better knowledge of their function and importance in the field of electronics. For engineers and physicists, it is important to understand capacitors for designing better circuits and fixing problems more successfully.

References

Tahalyani, J., Akhtar, M. J., Cherusseri, J., & Kar, K. K. (2020). Characteristics of capacitor: fundamental aspects. In Handbook of Nanocomposite Supercapacitor Materials I: Characteristics (pp. 1-51). Cham: Springer International Publishing.

Kaiser, C. J. (Ed.). (2012). The capacitor handbook. Springer Science & Business Media.

Sarjeant, W. J. (1989, September). Capacitor fundamentals. In Proceedings of the 19th Electrical Electronics Insulation Conference, (pp. 1-51). IEEE.

Westerlund, S., & Ekstam, L. (2002). Capacitor theory. IEEE Transactions on Dielectrics and Electrical Insulation1(5), 826-839.

Nishino, A. (1996). Capacitors: operating principles, current market and technical trends. Journal of power sources60(2), 137-147.

Sarjeant, W. J. J. Z. (2002). Capacitors. IEEE Transactions on Electrical Insulation25(5), 861-922.

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About Author

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Rabina Kadariya

Rabina Kadariya is a passionate physics lecturer and science content writer with a strong academic background and a commitment to scientific education and outreach. She holds an M.Sc. in Physics from Patan Multiple Campus, Tribhuvan University, where she specialized in astronomy and gravitational wave research, including a dissertation on the spatial orientation of angular momentum of galaxies in Abell clusters. Rabina currently contributes as a content writer for ScienceInfo.com, where she creates engaging and educational physics articles for learners and enthusiasts. Her teaching experience includes serving as a part-time lecturer at Sushma/Godawari College and Shree Mangaldeep Boarding School, where she is recognized for her ability to foster student engagement through interactive and innovative teaching methods. Actively involved in the scientific community, Rabina is a lifetime member of the Nepalese Society for Women in Physics (NSWIP). She has participated in national-level workshops and presented on topics such as gravitational wave detection using LIGO/VIRGO open data. Skilled in Python, MATLAB, curriculum development, and scientific communication, she continues to inspire students and promote science literacy through teaching, writing, and public engagement.

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